Electronic devices such as linear power amplifiers, multi-chip modules, electronic hybrid assemblies such as power amplifiers, microprocessors and passive components such as filters may contain heat sources which require cooling during normal operation.
Various techniques may be used for cooling electronic devices. Traditionally, electronic devices have been cooled by natural or forced air convection which involves moving air past heat sinks attached directly or indirectly to the devices.
Efforts to reduce the size of devices have focused upon increased integration of electronic components. Sophisticated thermal management techniques using liquids, which allow further abatement of device sizes, have often been employed to dissipate the heat generated by integrated electronics.
The cold plate is typically a direct replacement for an air-cooled heat sink in which water or another fluid flows through internal passages where the heat sink was originally mounted. This single-phase technique cools the whole surface of an electronic device, rather than primary heat sources, such as individual electronic components, located on the surface of the device. Cooling an entire electronic device may not be desirable or practical for several reasons. First, product designs may result in electronic components having various maximum operating temperatures being co-located--thus reducing the life of some electronic devices which are forced to function at higher than desired temperatures or reducing overall heat transfer efficiency when other electronic components are cooled below their reliable maximum operating temperatures. Second, cold plates' flow passages are generally highly complex, which makes it difficult to accurately predict heat transfer characteristics. Third, high fluid flow rates (up to several gallons per minute) may be required for successful application of cold plate technology.
Although two-phase cooling techniques such as evaporative spray cooling and heat pipes are preferred methods of heat removal in many electronics applications, heat sinks utilizing two-phase cooling techniques suffer from many of the same disadvantages as cold plates, typically having complex designs and providing for only one operating temperature for an entire heat sink.
There is therefore a need for a hybrid apparatus and method for cooling an electronic device which uses a two-phase cooling technique and also a conduction/convection technique, and which allows for localized cooling of devices or components having different optimal operating temperatures.